1. Field of the Invention
This invention relates to a mask pattern forming method, a fine pattern forming method and a film deposition apparatus which are used for semiconductor processes. More particularly, the invention relates to a mask pattern forming method, a fine pattern forming method and a film deposition apparatus which are capable of improving the precision to correct the pattern dimensions when forming patterns at pitches smaller than a resolution limit of an exposure device, without increasing the manufacturing cost.
2. Description of the Related Art
With high integration of semiconductor devices, wiring patterns and isolated widths required in manufacturing processes have come to be finer in size. Generally, in order to form a fine pattern, a resist pattern is formed by a photolithographic technique, and, by using the resist pattern as a mask of etching, a thin film formed beneath the resist pattern is etched. Therefore, the photolithographic technique is important for this purpose. However, the microstructures of the latest semiconductor devices have come to require a pitch of fine patterns which is below a resolution limit of the photolithographic technique.
In the following, a pattern which is used as the mask for forming a fine pattern by etching a thin film will be referred to as a mask pattern. This mask pattern may include a sacrifice film, such as an oxide film, and a resist film. Moreover, in the following, the term “fine pattern” may be used to indicate that it is inclusive of a mask pattern.
Patent Document 1 listed below discloses a technique for forming patterns at a pitch smaller than the resolution limit. In the technique of Patent Document 1, a first photoresist pattern (or a first resist pattern) is formed, baking of the first resist pattern is performed, and an oxide film is formed on the first resist pattern. Then, a second photoresist pattern (or a second resist pattern) is formed between the first resist patterns, and by using the first resist patterns and the second resist pattern as an etching mask, a thin film formed beneath the resist patterns is etched so that a fine pattern is formed.
According to the technique of Patent Document 1, fine patterns are formed using the two photo masks, and the resolution that is higher than that in the case of using one photo mask can be obtained. For this reason, the fine patterns with a pitch that is below the resolution limit can be formed according to the technique of Patent Document 1.
Recently, attention is focused on a technique in which a film deposition process to form a silicon oxide film on a pattern organic film is combined with SWT (side wall transfer process) or LLE (lithography-lithography etching process), as a fine pattern forming method to form fine patterns with a pitch below the resolution limit of the photolithographic technique.
Patent Document 2 listed below discloses a technique for use in the above-described fine pattern forming method to form an oxide film on a resist pattern. Although Patent Document 2 does not disclose a method of forming fine patterns with a pitch below the resolution limit, the technique of Patent Document 2 forms the oxide film on the resist pattern, which can prevent the thickness of the resist pattern from being decreased and prevent striation and wiggling from arising in the resulting fine patterns.
However, in the above-described fine pattern forming method in which the film deposition process to form the silicon oxide on the pattern organic film is combined with the fine patterns formed by SWT or LLE, the following problems will arise.
Because of the resolution limit of the photolithographic technique described above, it is necessary to perform an additional dimension correcting process (slimming, trimming, or smoothing) to correct the dimensions of the pattern organic film after the photolithographic process is performed. This will increase the manufacturing cost.
When the slimming, trimming or smoothing process is performed to correct the dimensions of the fine patterns, a resist coater, an asking device or an etching device must be used. When the film deposition process is performed, a film deposition apparatus must be used. For this reason, the semiconductor substrate (wafer) after the slimming process is finished is taken out from the ashing device, and it is conveyed to the film deposition apparatus.
However, if the wafer is taken out from the ashing device after the slimming process is finished, dust or foreign matter will adhere to the surface of the resist pattern. If dust or foreign matter adheres to the surface of the resist pattern, the density of defects in the silicon oxide film formed on the resist pattern will increase and the uniformity in thickness of the silicon oxide film will easily be loaded.
Moreover, when the slimming process or the film deposition process is performed, it is difficult to maintain the dimensions of resist patterns in order to make the difference between a top width and a bottom width of each resist pattern small. For this reason, it is difficult to form fine patterns with a good configuration.    Patent Document 1: Japanese Patent No. 2757983    Patent Document 2: Japanese Arranged-Open Patent Publication No. 2004-080033